Unity fbx export has resulted in a destroyed looking mesh
All you need to do is invert normals to right direction.

In edit mode:
Easiest way is select all faces by "A" > recalculate by "CTRL+N". This work in most cases. Usally does not work in non-closed/un-manifold meshes

Second way is manually select normals which you need invert and press "SPACE" > start typing "flip normals" > "Enter".